Intense research is being carried out worldwide with the goal of developing rapid, simple, specific, and sensitive detection tools for medical diagnostics and biomedical research applications. Fundamentally, most analytical tests and immunoassays rely on molecular recognition and its transduction into a measurable output. Among all the possible molecular recognition elements, artificial nucleic acid ligands (aptamers) have recently attracted a lot of interest due to their capability of binding various metal ions, amino acids, drugs, proteins, as well as other molecules having high affinity and specificity.1-11 
Aptamers are usually isolated from combinatorial libraries of synthetic nucleic acids by an iterative process of adsorption, recovery, and amplification coined as SELEX (Systematic Evolution of Ligands by Exponential Procedure). Aptamer-based ligands constitute highly promising candidates for the specific detection of various molecules. Additionally, they can also be used in competition binding assays, such as for example in high-throughput screening assays7, for the identification of new potential drugs capable of displacing the aptamers from their targets.
The above-mentioned approaches, however, require adequate transducing (i.e. reporting) elements in order to generate a physically measurable signal resulting from the recognition event. Binding of an aptamer to a target protein, for example, has been detected by using fluorescence (e.g. molecular beacons12-13) or by using a quartz microbalance14. In most cases, however, these methods either involve a tagging process or sophisticated experimental techniques. Furthermore, it is worth noting that labeling with various functional groups may even compromise the binding properties of the aptamers.
There thus remains a need to develop a rapid, simple, specific and sensitive detection tool capable of transducing the binding of an aptamer to its target into a clear signal.
The present invention seeks to meet these and other needs.
The present invention refers to a number of documents, the content of which is herein incorporated by reference in their entirety.